Creating a material similar to the art style of Gareth Davies @spudonkey
Firstly, you can try Edge nodes. http://blendernpr.org/edge-node-v1-2-4-july-2015/
I haven't tried it  myself but I think you can get the result you want. 
If that seems too much of a hassle (which it probably is), I've managed to get the colors to be passable as an imitation. Of course you would have to improve this greatly. Here is the setup: 

Play around with the noise and the mapping nodes to get diffirent color splashes. Also, it might be necessary for you to play with the Light path node in case the emmision shader's light is shown in other elements in your scene.
Hope this helps a little